The present invention relates to a new class of compounds having a gas-fixing activity, to a method for preparing said compounds, to methods for producing composite materials on various matrices and thin or thick films deposited on various substrates and containing said compounds, and to their use, as well as to a method for eliminating certain gases from a mixture that comprises them by using said compounds.
Various classes of materials with gas-fixing capabilities are currently known. They can be divided into two categories, depending on whether a) the fixing properties depend on actual chemical reactions, which entail the decomposition of the fixing material or b) the fixing properties depend on the adsorption characteristics at the physical surface of the fixer and, in general, on the size of the molecules to be fixed. Some typical examples of type a) materials are compounds capable of eliminating water vapor from a mixture of gases, for example calcium sulfate, phosphorus pentoxide, magnesium chloride, or carbon dioxide from a mixture of gases, for example sodium and potassium hydroxides and calcium, strontium, and barium oxides. Classic examples of type b) fixing materials are materials having an activated surface, such as activated charcoal or the various types of zeolite or some kinds of clay.
The fixing properties of type a) materials are selective, in that a compound is capable of fixing a single type of gas. The range of usable spontaneous reactions is rather limited and does not include gases which are highly harmful to the health and to the environment, such as nitrogen monoxide NO and carbon monoxide CO. Moreover, the involved reactions may be irreversible, so that the fixer loses all activity after a given utilization cycle.
On the other hand, type b) materials are not selective and fix gas molecules according to their size, degree of polarity, and relative molecular mass. These materials are unable to fix light molecules, such as the combustion products that are most harmful to the health and to the environment, such as mixtures of nitrogen oxides NO and NO2 and carbon oxides, particularly the monoxide CO.
A principal aim of the present invention is to eliminate the drawbacks of conventional materials having gas-fixing capabilities, with particular interest for the removal of noxious components from combustion products and more generally from gas mixtures.
This aim as well as other objects which will become apparent from the following detailed description of the invention are achieved by a class of compounds according to the invention, which is represented by a compound having the formula A2B3O6xc2x1d, wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide or a solid solution thereof; B is a transition metal, an element of group III, or a solid solution thereof; and d has a value between 0 and 1.
Advantageously, A is chosen from the group constituted by barium, cesium, potassium, strontium, a lanthanide, or solid solutions thereof.
Conveniently, B is chosen from the group constituted by copper, nickel, manganese, iron, palladium, titanium, aluminum, gallium, zinc, cobalt, or solid solutions thereof.